Fourteen Americans have been killed in the fighting in Israel, President Joe Biden announced Tuesday, and he confirmed more are among those being held hostage by Hamas terrorists.
"We now know that American citizens are among those being held by Hamas," Biden said. "I've directed my team to share intelligence and deploy additional experts from across the United States government to consult with and advise Israeli counterparts on hostage recovery efforts. Because as president, I have no higher priority than the safety of Americans being held hostage around the world."
Biden delivered remarks at the White House, which was lit up in blue and white on Monday evening in a show of support for Israel after Hamas launched a surprise air, sea and land incursion over the weekend.
Israel since declared a state of alert for war and has been sending retaliatory airstrikes to Gaza. The number of people killed on both sides is mounting.
MORE: Horrors emerge from Hamas infiltration of Israel on Gaza border"There are moments in this life, and I mean this literally, when pure, unadulterated evil is unleashed on this world," Biden said angrily as he spoke in the State Dining Room flanked by Vice President Kamala Harris and Secretary of State Antony Blinken. "The people of Israel lived through one such moment this weekend."
"The bloody hands of the terrorist organization Hamas, a group who stated purpose for being is to kill Jews," Biden continued. "This was an act of sheer evil. More than 1,000 civilians slaughtered, not just killed, slaughtered in Israel. Among them, at least 14 American citizens killed."
ABC News has not confirmed that total number of civilians killed in Israel, though it was repeated by national security adviser Jake Sullivan at the daily White House briefing. Sullivan said the administration did not have the exact number of Americans being held hostage but said 20 or more are considered "missing."
"We do not know about their condition, and we cannot confirm a precise number of American citizens," Sullivan said.
"We will work hour by hour, both to determine whether we can account for any of those Americans, or to confirm exactly what the number of Americans are being held hostage and we will come back too with that information as soon as we have it," Sullivan added.
Asked by ABC News Chief White House Correspondent Mary Bruce if Biden had spoken to any of the families of the 14 Americans killed, Sullivan said "not yet" but that the State Department has been in contact with them.
Sullivan added that Biden has been making it a priority to "ensure that we can secure the bodies of those that have perished and ensure that they get returned to their loved ones."
Ahead of his remarks, Biden and Harris met with their national security teams to get an update on the situation and give direction on "next steps." They also spoke with Israel Prime Minister Benjamin Netanyahu. Biden, who shared a photo of the meeting on social media, said the discussion with Netanyahu focused on "coordination to support Israel, deter hostile actors, and protect innocent people."
.@VP and I sat down with our teams to receive a situation update on the terrorist attack in Israel and to direct next steps.
— President Biden (@POTUS) October 10, 2023
We connected with Prime Minister Netanyahu to discuss coordination to support Israel, deter hostile actors, and protect innocent people. pic.twitter.com/u4xOHMeMqw
"We stand with Israel," Biden made clear as he addressed the nation. "And we will make sure Israel has what it needs to take care of its citizens, defend itself and respond to this attack."
Biden didn't mince words as he described the violence unfolding, describing "Hamas' bloodthirstiness" as reminiscent of ISIS rampages -- including "stomach churning reports of babies being killed."
But while he said, "Israel has the right to respond, indeed has a duty to respond to these vicious attacks," he also said he spoke with Netanyahu about how democracies like the U.S. and Israel "are stronger and more secure when we act according to the rule of law." Terrorists, he said on Tuesday, target civilians while democracies "uphold the laws of war."
Asked by ABC News White House Correspondent Karen Travers if Biden was giving a warning to Netanyahu as Israel signals it's moving to the next phase of its response, Sullivan bristled: "It was not a warning."
"It was two leaders talking to one another," Sullivan said. "One who is leading a nation that has suffered an unfathomable attack and another nation who is standing behind them square in the defense of their country."
White House national security spokesman John Kirby, during an appearance on ABC's "Good Morning America" earlier Tuesday, was asked if the U.S. would be willing to make a deal for any Americans who may be being held by Hamas. Kirby only said he "didn't want to get too far ahead of where we are."
"Clearly, the safety and security of Americans are a top priority for President Biden, we've seen that in the past," Kirby said. "We'll continue to work on this hard and if there are Americans that are being held hostage we'll do everything possible to get them home to their families where they belong."
MORE: Timeline of surprise rocket attack by Hamas on IsraelThe administration is boosting munitions to Israel, and the USS Gerald R. Ford aircraft carrier was sent toward Israel -- a move a senior U.S. defense official said was intended to be a deterrent to Iran and Hezbollah.
Iran has denied involvement in the Hamas attacks on Israel, and the U.S. and Israel have also said they don't have hard evidence linking Iran to the incursion.
Kirby on GMA was pressed about the threat of a second front opening up in the conflict if Hezbollah -- also designated a terrorist group by the U.S. and other nations -- were to engage.
"It remains unclear. Obviously, we are concerned about the possibility that now a northern front could be opened up if Hezbollah decides to get engaged," Kirby said. "Now, there's been some exchange of rocket fire, George, but no signs that they're all in as it as it were. So, we're watching this very, very closely."
Biden didn't address any specific nation or group, though he had a warning against "anyone thinking of taking advantage of this situation."
"I have one word: don't. Don't. Our hearts may be broken, but our resolve is clear," the president said.
-ABC's Justin Gomez contributed to this report.
